Milk allergy 'caused by Stone Age genes'

The one in 10 people who are unable to stomach milk because they are "lactose intolerant" should blame it on their Stone Age genes, scientists said yesterday.

A study of DNA from skeletons suggest that all European adults living between 6,000 BC and 5,000 BC were unable to absorb lactose – a sugar found in milk.

Their findings back the idea that the ability to digest milk spread only after the introduction of cattle farming in Europe 20,000 years ago.

The rival idea, that dairy farming was pioneered by a small group of Neolithic farmers who were able to tolerate milk, is overturned by the genetic study by a team from University College London and Mainz University, Germany.

Instead, the Neolithic descendants of Palaeolithic (Stone Age) people evolved their tolerance of milk within the last 8,000 years due to exposure to dairy products, making this "the most rapidly evolved European trait of the past 30,000 years," according to Dr Mark Thomas of UCL. "Lactose tolerance is very much a Neolithic invention."

To investigate the link between farming and lactose intolerance, the team focused on the DNA for a gene responsible for lactase, an enzyme needed to digest milk.

In their study, published in the Proceedings of the National Academy of Sciences today, Prof Joachim Burger, of Mainz, searched for the gene in the DNA extracted from the bones from 51 Neolithic people from the earliest organised European communities and found that it was missing.

This suggests that the first European cattle farmers used their herds for working the land, leather and meat. They moved on to yoghurt and cheese, which contain less lactose.

But, through exposure to milk, lactose tolerance – a persistent form of the lactase enzyme – evolved extremely rapidly so that it is now present in more than 90 per cent of the population of northern Europe.

It is also found in some African and Middle Eastern populations but is missing from the majority of the adult population globally. "The majority of Northern and Central Europeans can call a minority of lactase persistent dairying farmers that lived some 7.000 years ago their ancestors," said Prof Burger.

"The ability to drink milk is the most advantageous trait that's evolved in Europeans in the recent past," added Dr Thomas.